Wind energy is increasingly recognized as a viable option for complementing and even replacing other types of energy such as fossil fuels. In the early development of wind energy, the majority of wind turbines or wind turbine generators (WTGs) were constructed for operation at a constant speed, but more recently, the trend is toward sing variable-speed wind turbines to better capture available wind power. In most cases, wind turbine pitch angles can be adjusted to control the operation of the variable speed wind turbine.
Wind turbine manufacturers use variable-speed turbines to capture available wind power over a wide range of wind speeds. To be effective, though, these variable speed wind turbines require active control systems to react to changing wind and other operating conditions. One concept that is fundamental to the control dynamics for a wind generator is that changing speed is a relatively slow process due to the large inertia values involved, and this makes it difficult to use a power converter in the turbine or in the turbine's “plant” to control the rotor speed. As a result, manufacturers and operators of variable speed wind turbines also use pitch control on an ongoing basis to regulate power flow at the high speed limit. In other words, a control system is used to vary pitch rapidly in response to rotor speed, and significant efforts have been made to improve this ongoing pitch control system.
Manufacturers and operators of wind turbines are also interested in setting a “nominal” pitch for wind turbines to allow the wind turbine to better capture available wind power when operating below rated speed and power. The nominal pitch can be thought of as a default set point to which the blades of a variable speed wind turbine are adjusted in order for the wind turbine to operate generally at a high efficiency. The control system may then vary the pitch of the blades from this nominal pitch in a relatively rapid manner to control power generation in response to wind gusts and other more rapid wind variations. Models have been generated by designers of wind turbines that predict the performance of wind turbines having particular blade configurations, and these models have been used to predict an optimal pitch for use as the nominal pitch for the wind turbine. Typically, the operator will then set this pitch with the control system as the nominal pitch. Some work has been performed to provide adaptive control of torque gain, but that work has assumed a particular nominal pitch.
Existing methods of selecting the nominal pitch for variable wind speed turbines have not been entirely effective. The models that have been used to predict wind turbine behavior have been shown by operating data and experimental results to be at least partially inaccurate, e.g., the models do not predict actual operating conditions and power generation results for most wind turbines. These inaccuracies may result in the nominal pitch being set too high or too low, which results in less than optimal capture of the available wind power. Additionally, the predictive models are useful for predicting operating parameters for a wind turbine based on design parameters. However, the installed wind turbine may not match the design parameters and its operating parameters likely will vary over time, such as due to pitting of the blades, due to weight variances of the blades (e.g., due to condensation or the like within the blades), due to variances in the generator components, or due to other operating conditions that change over time and in response to physical conditions. Further, tolerances in sensors and controls may affect actual operating results, e.g., a sensor or blade actuator indicating a particular pitch for a blade may be inaccurate which may result in the blade being set at a pitch that varies from the control setting.
Due to these ongoing challenges with controlling pitch of wind turbine blades, there remains a need for improved methods and systems for adaptively controlling pitch of blades in variable speed wind turbines. Preferably, such methods and systems would be configured for implementation with existing plant or generator control systems, e.g., to utilize existing wind speed, rotor speed, mechanical power generated, and other operating parameter sensors and signals and existing plant or turbine control systems including blade pitch actuators.
The foregoing examples of the related art and related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.